Can't speak to the new 13" MacBook Air (at least until mine arrives next week) but my 2008 Air has an SSD and the combo of that and the rigid aluminum body led me to abandon my Brain Cell for a Cache for daily carry and air travel. i've had no trouble at all getting my Air into or out of the Cache, nor can I imagine a circumstance in daily use in which the flap-tucked-in Cache would allow the Air to slip out accidentally: you have to work at it (and I just tried). The tremendous up side of the Air-Cache combo is a large amount of extra space in your carry on and a TSA-friendly time at the x-ray machines. I typically slip my Air/Cache into the open back pocket of my ID while waiting on the security line, pop it into a tray for the trip through x-ray, then zip it back up in the ID's main compartment once I'm screened.
Now that I have my MacBook Air (13") and cache, I can report that the MBA fits very snugly and is very secure. On this week's trip I took the Air and iPad in their caches, carrying them in the Swift. Worked out very nicely!
One thing I noticed is that the cache was a little too snug at first, but after taking the MBA in and out of the cache a few times, the cache loosened up a bit and now it works like a charm--very easy to put the computer in and take it out, while holding providing a nice secure case.